This invention relates to an image receiving sheet for thermal transfer recording, which can receive a thermally transferred dye, more specifically to an image receiving sheet for thermal transfer recording, which can provide a high density transferred image and can maintain the transferred dye image stably relative to heat and light.
In the prior art, there has been known a thermal transfer system in which a dye or an ink is transferred by a heat source such as a thermal head or a laser. Recently, attention has been paid to a thermal transfer system using a sublimable dye (or a thermally diffusible dye). The transfer system using these dyes has an advantage that gradation can be given to picture elements by controlling energy of a heat source, whereby it has been used more widely as a means for obtaining a color image with high image quality.
However, in the sublimation type thermal transfer system, much energy is required to sublimate or thermally diffuse a dye, so that progress of techniques concerning sensitivity has been expected. Further, storage stability of an image is inferior to that of the so-called silver halide photography which has been highly completed, so that high durability of a transferred image has been demanded.
As a means for improving sensitivity, there has been proposed a technique of plasticizing a binder in a dyeing image receiving layer to be used in an image receiving sheet for thermal transfer recording (by adding the so-called heat solvent or internally plasticizing a binder) to improve diffusibility of a dye. However, storage stability of an image relative to heat is worsened due to increased diffusibility of a dye, whereby evil influences such as bleeding of an image are brought about.
Thus, there has been proposed a system in which a chelate type dye is used as a dye to be transferred, and the dye has a small molecular weight during transfer and reacts with a metal compound in an image receiving layer after transfer to form a chelate dye. According to this system, a selection range of a binder can be broadened to a great extent as compared with the case where a conventional dye is used. However, there is a limit in plasticizing a binder in an image receiving layer, and when a glass transition temperature (Tg) is extremely small, there is a problem that blocking of an image receiving sheet for thermal transfer recording is caused.